Cutting Tempered Glass
Can You Cut Tempered Glass? We are often asked if we can cut glass that has already been tempered. Unfortunately, the answer to this question is no. All fabrication is done prior to tempering. That means we cut your glass to your exact size, fabricate any holes and notches needed, miter, then polish the glass resulting in a final piece of glass. Tempered glass is regular glass that has been heat treated to increase strength and thermal shock resistance to prevent injury by changing the break pattern. Tempered glass is used in applications where heat, mechanical strength and safety are a factor. For example, the glass on motor vehicles is tempered to make it strong and less dangerous when it shatters or breaks. Tempered glass is also used in fireplace doors, on masonry and prefabricated fireplaces equipped with a grate to hold the burning wood. Tempered glass can withstand constant temperatures of 470°F. If tempered glass is exposed to higher temperatures, it gradually weakens the structure of the glass thus making it more susceptible to breakage. If a piece of tempered glass is exposed to continuous temperatures of 600°F or more, the glass will shatter into small pieces.
Glass Weight Formulas
Glass Weight per Square Foot (multiply width by height and divide by 144)
1/8" = 1.64 lbs.sq.ft.
3/16" = 2.45 lbs.sq.ft.
1/4" = 3.27 lbs.sq.ft.
3/8" = 4.91 lbs.sq.ft.
1/2" = 6.54 lbs.sq.ft.
3/4" = 9.84 lbs.sq.ft.
1" = 13.11 lbs.sq.ft.
How Mirrors are Made
When most people use the term "mirror," they are referring to what is known as a plane mirror. A plane mirror takes the light that hits it and reflects it back. Mirrors used for common consumer purposes are of this sort. A mirror is essentially a highly reflective surface. The sorts of mirrors one sees on walls or in bathrooms are of a type known as back-silvered mirrors. This means that the reflective surface--in most modern mirrors this is aluminum--is viewed through a thin layer of glass. The glass protects the aluminum from scratching and bubbling, but also distorts the image somewhat. Early mirrors were created by simply polishing a suitable substance until it became highly reflective. Neolithic mirrors have been discovered, made by grinding down obsidian rocks and polishing them to an incredible sheen. These mirrors have remarkable properties, allowing even subtle details to be clearly seen in their reflections. Modern mirrors, however, are made using an entirely different process. By taking liquid metals and allowing them to condense on a sheet of glass, one can get a surface far more reflective than anything achieved by polish. Making a mirror can be done at home with only a few supplies easily acquired at a local chemistry shop. With pure silver nitrate, distilled water, and ammonia, one can make a mirror virtually indistinguishable from those purchased at a store. The process (in abbreviated form) involves dissolving a small amount of silver nitrate in distilled water, then adding diluted ammonia until the mixture goes through distinct chemical changes. A second mixture is made using silver nitrate and Rochelle salts. This mixture must be boiled and filtered. By pouring these mixtures on to a very clean piece of glass sufficiently heated to the proper temperature, the silver will precipitate and form an even coating on the glass. After drying, one can coat the back of the silver with a solid paint to help prevent degradation of the silver. The result is a fully functional mirror. Commercial mirrors are manufactured in more or less the same manner as is described above, though materials such as aluminum might be used instead of silver. Mirrors produced for specialized purposes, such as lasers or telescopes, are manufactured using much more exacting techniques to acquire a much more precise mirror, but the general principles remain the same.
Strength of Glass
Uniform load strength - Heat-Strengthened Glass
Note: Data obtained from Fed. Spec. DD-G-1403.
The values have not been verified
|Nominal Glass Thickness. mm (in)||Average Breaking
Pressure times Glass Area.
Pa x m2 (lbf x ft2). Minimum value
|3mm (1/8")||5895 (1,325)|
|5mm (3/16")||14,800 (3,325)|
|6mm (1/4")||24,000 (5,400)|
|8mm (5/16")||32,700 (7,350)|
|10mm (3/8")||55,000 (12,000)|
|12mm (1/2")||70,000 (16,000)|
Laminated - A process by which two or more lites of glass are sandwiched about a polyvinyl layer to give the glass strength against penetration. It is not shatter proof or unbreakable. The most common application that everyone should be familiar with is automobile windshields.
Tempered - The process of heat-treating glass, to provide much stronger characteristics than annealed, or un-tempered glass. Once again, tempered glass is not shatter proof or unbreakable. It is designed to break into very small pieces to help alleviate severe lacerations. This process is used on automobile side and rear windows as well as storefronts and doors that are required by local building codes.
Please check with your county for any questions regarding local building codes.